The present invention relates to a novel production method of tris(pentafluorophenyl)borane using pentafluorobenzene as its starting material. The boron derivatives obtainable by the invention are extremely serviceable compounds as an auxiliary catalyst for cationic complex polymerization, and also as intermediates of N,N-dimethylauilinium tetrakis(pentafluorophenyl)borate which is useful as an auxiliary catalyst for cationic complex polymerization.
In recent years, scientific literatures or patents for conducting polymerization reactions using these compounds and organometallic complexes have increased remarkably; e.g. J. Am. Chem. Soc., 113, 3626 (1991), Macromol. Chem. Rapid Commun., 2, p. p. 663-667 (1991) or the like. However, for the production of tris(pentafluorophenyl)borane, relatively expensive bromopentafluorobenzene has been used conventionally as a starting material for the source of pentafluorophenyl group.
The method was such that bromopentafluorobenzene was subject to a bromine-metal exchange reaction at a low temperature of -70.degree. C. using organometallic compounds such as butyllithium to generate pentafluorophenyllithium (J. Org. Chem., 29, 2385 (1964), J. Org. Chem., 31, 4229 (1966) and Synthesis of Fluoroorganic Compounds, p. 190, Springer-Verlag (1985)), which was reacted with boron trichloride, boron trifluoride or the like as a starting raw material for the boron source, or bromopentafluorobenzene was reacted with magnesium to generate Grignard's reagent such as pentafluorophenylmagnesium bromide (J. Chem. Soc. 166 (1959), Z. Naturforschg., 20b, 5 (1965) and Synthesis of Fluoroorganic Compounds, p. 141, Springer-Verlag (1985) etc.), which was reacted similarly with boron trichloride, boron trifluoride or the like as a starting raw material for the boron source, thereby producing tris(pentafluorophenyl)borane (J. Organometallic Chem., 2, 245-250 (1964)).
Bromopentafluorobenzene can be obtained by brominating pentafluorobenzene. However, if it would be possible to produce tris(pentafluorophenyl)borane directly from pentafluorobenzene, the production processes could be reduced by one process leading to easier availability and also lower price of starting raw material. On the other hand, literatures for generating pentafluorophenylmagnesium bromide for the reaction using pentafluorobenzene as a starting raw material have already been published (J. Chem. Soc., 166 (1959), Synthesis of Fluoroorganic Compounds p141, J. Org. Chem., 29, 2385 (1964) and ibid, 31, 4229 (1966), but the production of tris(pentafluorophenyl)borane has been unknown.
In view of the situation aforementioned, the inventors have so extensively investigated that the brominating process of pentafluorobenzene may be eliminated by changing the use of bromopentafluorobenzene, which has been used as a starting material for the production of tris(pentafluorophenyl)borane, to that of pentafluorobenzene, further the cost for the production installation may be decreased by making the very low temperature such as -70.degree. C. at the time of generating pentafluorophenyllithium from bromopentafluorobenzene to be unnecessary, and further the use of relatively expensive reacting agent such as organolithium compound may be omitted, thus leading to the present invention.